In numerous situations, electric motors are subjected to vibrations which may result from the operation of the motor itself or which may come from the environment of the motor, for example when this motor is placed next to a vehicle or a machine which is itself subjected to numerous vibrations.
When normal operation of the motor is accompanied by vibrations of high frequency and intensity, it has been found that the braid could become detached from the wearing part, causing a stoppage of the motor which could have the most serious consequences.
This has been found, in particular, with the most economical brushes of simple design obtained by mere compression of electrically conductive powder, in which the braid is fixed to the wearing part merely by immersing the braid in the powder during compression of the conductive powder.
On the other hand, brushes of a more elaborate design which typically involve several stages of manufacture and are therefore more expensive than the previous ones, for example brushes of which the braid is brazed to the wearing part, are better at withstanding intense vibrations.
Attempts have already been made to solve the problem posed, that is to obtain brushes which are both economical and resistant to intense vibrations.
Thus, German patent 2 322 713 proposes various solutions for solving this problem.
According to one solution proposed, an elastic housing is provided at the point of the connection, the housing being composed of an elastic part.
According to another solution, an additional mass is adjoined to the braid in the vicinity of the connection.
A further solution involves injecting plastics material into the braid.
Finally, this patent proposes, for the connection, a housing which widens as the surface of the brush is approached.
The inventors have found that although some of these solutions improved the resistance of the connection to vibrations, in particular those involving the addition of a plastic part, the addition of a plastic part can give rise to a problem of heat resistance in a considerable number of cases, not to mention the extra manufacturing cost.